In an OFDMA/SC-FDMA based system the available bandwidth is sub-divided into several resource blocks or units as defined, for example in 3GPP TR 25.814: “Physical Layer Aspects for Evolved UTRA”. According to this document a resource block is defined in both time and frequency. In the downlink each user terminal estimates the downlink channel quality on each resource block and reports the measured quality to the network. The downlink channel quality can be indicated by various types of measurements carried out by the terminal, such as channel quality indicator (CQI), received signal strength indicator (RSSI), transmit power of the terminal, signal to interference and noise ratio (SINR) etc.
In the uplink on the other hand, the base station, often referred to as Node B, can carry out various types of measurements such as downlink total transmit carrier power, downlink transmit carrier power per resource block, uplink received total wide band power, resource block usage etc. Based on the measurements reported by the terminal and the measurements performed by the base station, the network can dynamically allocate or schedule the resource blocks to the users for data transmission. The network also utilizes these measurements to perform other types of radio resource management tasks such as handover, congestion control, admission control etc.
In CDMA systems each user is allocated the entire bandwidth but different users are distinguished by assigning a separate orthogonal and/or scrambling code. However in OFDMA/SC-FDMA systems, each cell possesses several resource blocks depending upon the system bandwidth. This is because the bandwidth of a resource block is much smaller than that of the system bandwidth. In an E-UTRA, according to the current working assumption, the resource block comprises of 180 kHz in frequency and 0.5 ms in time. As an example there will be 48 and 96 resource blocks for 10 MHz and 20 MHz respectively since some portion of the bandwidth acts as guard band and is therefore left unused. Some radio resource management functions such as scheduling, inter-cell interference coordination, congestion control etc would require the terminal and the base station to carry out various kinds of measurements on each or on a group of resource blocks. Furthermore, in order to track fast temporal channel variations the measurements are to be reported quite frequently, such as every transmission time interval (TTI), which is 1 ms. This would involve considerable signalling overheads leading to capacity loss.
In E-UTRA, different types of measurements from a base station may be reported to several neighbouring base stations. This would lead to duplication of measurement reports over mesh type network such as in E-UTRA, where all the base stations are logically connected to each other. This would imply considerable signalling overheads over the interfaces between the base stations. It has therefore been proposed to multicast measurements to a group or a set of base stations that has joined the distribution list. This implies that measurements from different base stations shall be multicast to several set of base stations.
International Patent Application No PCT/SE2005/001579 discloses a method for reducing the signalling load especially on the radio interface in E-UTRA by reporting measurements in differential manner, that is, reporting each measurement value as a difference between the measurement value and a maximum value defined for the relevant type of measurement. This differential method is also described in 3GPP TR 25.814: “Physical Layer Aspects for Evolved UTRA”.
The state of the art solution reduces the signalling overheads for each measurement individually. However in the current system a terminal may have to report several different kinds of measurements. Similarly each base station may report several types to measurements to its neighbouring base stations. This means there will still be considerable overhead due to measurement reporting.